CN103605090A - Demagnetization detection method, demagnetization detection circuit and constant current driver using circuit - Google Patents
Demagnetization detection method, demagnetization detection circuit and constant current driver using circuit Download PDFInfo
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Abstract
The invention provides a demagnetization detection circuit (10). The demagnetization detection circuit (10) comprises a voltage drop unit (11), a reference level generating unit (12) and a comparison unit (13), wherein the voltage drop unit (11) is connected with a drain electrode end (DRAIN) of a power switch transistor (M1) to be detected and used for reducing the voltage of a signal from the drain electrode end (DRAIN) and sending a drain electrode signal (Vx) obtained after the voltage drops to the comparison unit (13); the reference level generating unit (12) generates a reference threshold value (Vref_DM) and sends the reference threshold value (Vref_DM) to the comparison unit (13); different input ends of the comparison unit (13) receive the drain electrode signal (Vx) obtained after the voltage drops and the reference threshold value (Vref_DM) respectively, and the comparison unit (13) compares the drain electrode signal (Vx) obtained after the voltage drops with the reference threshold value (Vref_DM) to detect the demagnetization end time. The inductance demagnetization time can be detected at the drain electrode end of the power switch transistor in a constant current driving circuit with the demagnetization detection circuit.
Description
Technical field
The present invention relates to a kind of demagnetization detection method and circuit, in particular to a kind of inductance demagnetization time detecting method and testing circuit driving for constant current, and the constant-flow driver of applying this circuit.
Background technology
Light emitting diode (light-emitting diode, LED), because of features such as its luminescence efficiency are high, the life-span is long, is used to lighting source at present more and more.Commercial or home light fixture is often driven by civil power (high pressure industrial-frequency alternating current), and this just need to be changed as LED steady current is provided by AC-DC.
AC-DC LED drive circuit (driver) is exactly in fact the constant-current power supply circuit of LED, it is luminous with driving LED that this circuit is converted to specific output current by civil power, and utilize device to modulate output current, so that output average current keeps constant, and output current does not fluctuate with the fluctuation of input voltage.AC-DC LED drive circuit is divided into two kinds of non-isolation type and isolated forms.
Chinese invention patent application No.200910246151.4 discloses a kind of " output voltage and inductance value change the source class driving LED driving circuit that keeps constant current ".In the disclosed LED drive circuit of this patented claim, when opening, second switch transistor sets the peak value of output current by comparer; During shutoff, by inductive current zero-crossing detector, detect inductive current, thereby second switch transistor is reopened at output current to zero time, assurance system works is under critical continuous conduction mode, and output current is only determined by peak point current.In this circuit, adopt source drive, the grid of the first switch mos transistor is fixed on to a lower voltage, thereby its source electrode ceiling voltage is limited in to a lower level, to adopt low pressure process to detect the waveform of the source electrode of the first switch mos transistor, find out the critical working point of electric current, guarantee that drive circuit works is at critical continuous conduction mode.
In being similar to the disclosed LED drive circuit of Chinese invention patent application No.200910246151.4, because the drain electrode ceiling voltage of detected power switch pipe is than a busbar voltage high diode drop also, up to several hectovolts, directly in drain electrode, detect demagnetization end point very difficult, both uneconomical, be also not easy to realize.
Summary of the invention
According to embodiments of the invention, a kind of demagnetization detection method and circuit are provided, the drain electrode end of the power switch pipe that application the method and circuit can be in constant-current drive circuits detects the inductance demagnetization time.
According to an aspect of the present invention, provide a kind of demagnetization of the inductance for constant-flow driver time detecting method, having comprised: reduce the voltage from the signal of measured power switching tube drain electrode; Generating reference threshold value; And by the drain signal of lower voltage and reference threshold comparison, detect demagnetization end time point.
According to the inductance demagnetization time detecting method of the embodiment of the present invention, alternatively, when the amplitude of the drain signal of lower voltage is during lower than the amplitude of reference threshold, demagnetization end time point detected.
According to another aspect of the present invention, a kind of demagnetization testing circuit is provided, comprise: pressure drop unit, datum generating unit and comparing unit, wherein, pressure drop unit is connected with the drain electrode end of measured power switching tube, for reducing the voltage of the signal from this drain electrode end, and the drain signal after step-down is sent to comparing unit; Datum generating unit generating reference threshold value, and this reference threshold is sent to comparing unit; The different input ends of comparing unit receive respectively drain signal and the reference threshold after step-down, and comparing unit compares the drain signal after step-down and reference threshold, detect demagnetization end time point.
According to the demagnetization testing circuit of the embodiment of the present invention, alternatively, pressure drop unit is further connected between the drain electrode end and internal electrical source of measured power switching tube, and when the voltage of drain electrode end is high level, this drain electrode end is that internal electrical source is powered by pressure drop unit.
According to the demagnetization testing circuit of the embodiment of the present invention, alternatively, pressure drop unit comprises voltage drop element, the input end of this voltage drop element is connected with the drain electrode end of measured power switching tube, its output terminal is connected to an input end of comparing unit, and between the output terminal of voltage drop element and internal electrical source, be further in series with diode and/or resistance, wherein the positive pole of diode is connected to voltage drop element one side, and its negative pole is connected to internal electrical source one side.
According to the demagnetization testing circuit of the embodiment of the present invention, alternatively, voltage drop element is technotron or isolated gate FET.
According to the demagnetization testing circuit of the embodiment of the present invention, alternatively, reference threshold is constant datum or unsteady datum.
According to the demagnetization testing circuit of the embodiment of the present invention, alternatively, between the input end of voltage drop element and output terminal, be parallel with electric capacity.
According to a further aspect of the invention, a kind of control circuit for constant-flow driver is provided, comprise: above-mentioned demagnetization testing circuit, constant current algorithmic controller, PWM controller, peak detctor and driving stage, wherein, demagnetization testing circuit is connected with the drain electrode of the power switch pipe of constant-flow driver, and with the drain signal of received power switching tube, and this demagnetization testing circuit sends a signal to constant current algorithmic controller after demagnetization end time point being detected; The demagnetization end time point that constant current algorithmic controller detects based on demagnetization testing circuit sends the first control signal to PWM controller; Peak current detector is carried out the source-drain electrode electric current of detection power switching tube by detecting the voltage of the sampling resistor of constant-flow driver, and to PWM controller, sends the second control signal according to this current detecting result; PWM controller generates pwm signal based on the first control signal and/or the second control signal, and this pwm signal is sent to driving stage; The output terminal of driving stage is connected with the grid of power switch pipe, with according to pwm signal conducting or turn-off this power switch pipe.
According to a further aspect of the invention, provide a kind of constant-flow driver, it comprises: resistance, and electric capacity, fly-wheel diode, inductance, power switch pipe and sampling resistor, wherein, resistance and capacitances in series are between bus and ground; The negative pole of fly-wheel diode is connected to positive pole and the bus of load light emitting diode; One end of inductance is connected to the positive pole of fly-wheel diode, and the other end is connected to the negative pole of load light emitting diode; Power switch pipe is connected between inductance and sampling resistor, and its drain electrode is connected to the positive pole of fly-wheel diode, and source electrode is connected to sampling resistor; One end of sampling resistor is connected with the source electrode of power switch pipe, other end ground connection, and driver also comprises aforesaid control circuit.
According to the constant-flow driver of the embodiment of the present invention, alternatively, if this constant-flow driver works in discontinous mode, when the pwm signal of PWM controller is while being high, the conducting of driving stage driving power switching tube, the drain voltage of power switch pipe is low level, electric current from bus through light emitting diode, inductance, power switch pipe, sampling resistor is to ground, the electric current of inductance increases gradually, correspondingly the voltage of sampling resistor also increases gradually, when sampling resistor voltage reaches predetermined threshold, peak current detector is sent the second control signal to PWM controller, PWM controller drags down pwm signal, make power switch pipe cut-off, pwm signal is that low time point is the starting point of demagnetization time, after power switch pipe cut-off, its drain voltage raises, and inductance is connected with fly-wheel diode and light emitting diode and formed a loop, and inductive current reduces gradually, when inductive current is reduced to zero, at the drain electrode generation ringdown of power switch pipe, demagnetization testing circuit detects this ringdown, thereby the end point of demagnetization time detected, detect demagnetization finish after, demagnetization testing circuit output signal to constant current algorithmic controller, at inductive current, remain after zero a period of time, constant current algorithmic controller sends the first control signal to PWM controller, and it is high making pwm signal, starts next cycle.
According to the constant-flow driver of the embodiment of the present invention, alternatively, demagnetization testing circuit is set to, and after pwm signal is low, through one section of delay, starts to detect again.
According to the constant-flow driver of the embodiment of the present invention, alternatively, if this constant-flow driver in critical current mode pattern, control circuit is set to, and when the electric current of inductance being detected, is zero, pwm signal is set to height immediately, starts next cycle.
According to a further aspect of the invention, provide a kind of constant-flow driver, having comprised: resistance, electric capacity, fly-wheel diode, power switch pipe, sampling resistor and isolating transformer, wherein, resistance and capacitances in series are between bus and ground; The armature winding of isolating transformer is connected between bus and power switch pipe, and its secondary winding is connected with the positive pole of fly-wheel diode; The negative pole of fly-wheel diode is connected to the positive pole of load light emitting diode; Power switch pipe is connected between the armature winding and sampling resistor of isolating transformer, and its drain electrode is connected to the armature winding of isolating transformer, and source electrode is connected to sampling resistor; One end of sampling resistor is connected with the source electrode of power switch pipe, other end ground connection, and driver also comprises aforesaid control circuit.
Accompanying drawing explanation
In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, below the accompanying drawing to embodiment is briefly described, apparently, the accompanying drawing in the following describes only relates to some embodiments of the present invention, but not limitation of the present invention.
Fig. 1 shows the schematic diagram of the testing circuit that demagnetizes according to an embodiment of the invention;
Fig. 2 shows the schematic diagram of the testing circuit that demagnetizes in accordance with another embodiment of the present invention;
Fig. 3 shows an example of the demagnetization testing circuit principle based on shown in Fig. 2;
Fig. 4 shows another example of the demagnetization testing circuit principle based on shown in Fig. 2;
Fig. 5 shows according to the basic circuit diagram of the non-isolation AC-DC LED driver of the embodiment of the present invention;
The sequential chart of Fig. 6 schematically shows the working condition under discontinous mode according to the AC-DC LED driver of the embodiment of the present invention;
The sequential chart of Fig. 7 schematically shows the working condition under critical current mode pattern according to the AC-DC LED driver of the embodiment of the present invention;
Fig. 8 shows according to the basic circuit diagram of the isolation AC-DC LED driver of the embodiment of the present invention.
Embodiment
For making object, technical scheme and the advantage of the embodiment of the present invention clearer, below in conjunction with the accompanying drawing of the embodiment of the present invention, the technical scheme of the embodiment of the present invention is clearly and completely described.Obviously, described embodiment is a part of embodiment of the present invention, rather than whole embodiment.Based on described embodiments of the invention, all other embodiment that those of ordinary skills obtain under the prerequisite without creative work, belong to the scope of protection of the invention.
Unless otherwise defined, technical term used herein or scientific terminology should be and in field, have the ordinary meaning that the personage of general technical ability understands under the present invention." first " of using in patent application specification of the present invention and claims, " second " and similar word do not represent any order, quantity or importance, and are just used for distinguishing different ingredients.Equally, the similar words such as " " or " " do not represent restricted number yet, and mean and have at least one.
Fig. 1 shows the testing circuit that demagnetizes according to an embodiment of the invention.Demagnetization testing circuit 10 shown in Fig. 1 comprises pressure drop unit 11, datum generating unit 12 and comparer 13.In Fig. 1, DRAIN represents the drain electrode end of tested switching tube, and VDD is chip internal power end.As shown in Figure 1, the input end of pressure drop unit 11 is connected with DRAIN, and its output terminal is connected to the inverting input of comparer 13; The input end of datum generating unit 12 is connected to VDD, and its output terminal is connected to the normal phase input end of comparer 13.Alternatively, also can adopt such connected mode, the output terminal of pressure drop unit 11 is connected to the normal phase input end of comparer 13, and the output terminal of datum generating unit 12 is connected to the inverting input of comparer 13.
As previously mentioned, the voltage of DRAIN end can reach several hectovolts.Due to the hypotensive effect of pressure unit 11, at the output terminal (Vx end) of pressure unit 11, produce the low voltage signal of about tens volts.After inductive current is reduced to zero, there is ringdown in DRAIN, under the effect of pressure unit 11, and the ringdown that there will be a voltage amplitude to reduce at Vx end.When voltage Vx lower than by datum generating unit 12, generated threshold value Vref_DM time, represent that demagnetization end point detection has arrived, comparer 13 output signal Vout.Wherein, Vref_DM can be constant datum, can be also the inner unsteady datum producing as calculated.
Due to the hypotensive effect of pressure unit 11, datum generating unit 12 and comparer 13 can be low-voltage circuits, are convenient to realize, and cost is also low.
In addition, the comparer 13 in embodiment illustrated in fig. 1 is voltage-type comparer, and it can be also current type comparator.Fig. 2 shows the testing circuit that demagnetizes in accordance with another embodiment of the present invention.Different from the embodiment shown in Fig. 1, in the demagnetization testing circuit 10 shown in Fig. 2, an output terminal of pressure drop unit 11 (output terminal that is different from Vx end) is connected to VDD.Particularly, the input end of pressure drop unit 11 is connected with DRAIN, output terminal of pressure drop unit 11 and the input end of datum generating unit 12 are connected to VDD, the output terminal of datum generating unit 12 is connected to the normal phase input end of comparer 13, and another output terminal of pressure drop unit 11 (Vx end) is connected to the inverting input of comparer 13.Alternatively, also can adopt such connected mode, the Vx end of pressure drop unit 11 is connected to the normal phase input end of comparer 13, and the output terminal of datum generating unit 12 is connected to the inverting input of comparer 13.
According to the embodiment of Fig. 2, when the drain electrode end DRAIN of tested switching tube voltage Vd is high level, the drain electrode of switching tube is powered to vdd terminal by pressure unit 11.Due to the hypotensive effect of pressure unit 11, at the output terminal (Vx end) of pressure unit 11, produce the low voltage signal of about tens volts.After inductive current is reduced to zero, there is ringdown in DRAIN, under the effect of pressure unit 11, and the ringdown that there will be a voltage amplitude to reduce at Vx end.When voltage Vx lower than by datum generating unit 12, generated threshold value Vref_DM time, represent that demagnetization end point detection has arrived, comparer 13 output signal Vout.Wherein, Vref_DM can be constant datum, can be also the inner unsteady datum producing as calculated.
Due to the hypotensive effect of pressure unit 11, datum generating unit 12 and comparer 13 can be low-voltage circuits, are convenient to realize, and cost is also low.
In addition, the comparer 13 in embodiment illustrated in fig. 2 is voltage-type comparer, and it can be also current type comparator.
Demagnetization testing circuit shown in Fig. 2 can, when DRAIN is high level, be VDD power supply; Due to the hypotensive effect of pressure unit, the high-voltage signal of DRAIN is reduced to the low-voltage signal of Vx end, for the realization of testing circuit provides condition; With low-voltage circuit, realized the detection of demagnetization end point.
Fig. 3 shows an example of the demagnetization testing circuit principle based on shown in Fig. 2.With Fig. 2 contrast, the demagnetization testing circuit 10a shown in Fig. 3 has comprised that pressure drop unit 11a(is as shown in dashed rectangle).In the example of Fig. 3, pressure drop unit 11a comprises high voltage bearing technotron JFET, and the diode D that connected between JFET and VDD.Wherein, the input end of JFET is connected with switching tube DRAIN, the output terminal of JFET is connected with the positive pole of diode D, the input end of the negative pole of diode D and datum generating unit 12 is connected to VDD, the output terminal of datum generating unit 12 is connected to the normal phase input end of comparer 13, and the output terminal of JFET is connected to the inverting input of comparer 13.Due to the interception (the unidirectional general character) of diode, when the drain terminal voltage Vd of tested switching tube is low level, VDD can oppositely not power to DRAIN, can keep better VDD constant like this.Similarly, also can replace diode D with the tandem compound of resistance or resistance and diode.
Alternatively, also can adopt such connected mode, the output terminal of JFET is connected to the normal phase input end of comparer 13, and the output terminal of datum generating unit 12 is connected to the inverting input of comparer 13.
Because drain electrode, the source electrode of JFET can exchange, if therefore using its source electrode as its input end, its drain electrode is output terminal, if drained as input end, its source electrode is output terminal.
In addition, as shown in Figure 2, the grounded-grid of JFET.Alternatively, the grid of JFET is connected to certain fixing bias voltage.
When DRAIN is high level, the drain electrode of switching tube is powered to VDD by JFET and diode D.Due to the hypotensive effect of JFET, at the output terminal (Vx end) of JFET, produce the low voltage signal of about tens volts.After inductive current is reduced to zero, there is ringdown in DRAIN, due to the coupling of the stray capacitance Cds between the source class of JFET and drain electrode, at Vx, holds and also there will be an amplitude to reduce ringdown.When voltage Vx lower than by datum generating unit 12, generated threshold value Vref_DM time, represent that demagnetization end point detection has arrived, comparer 13 output signal Vout.Wherein, Vref_DM can be constant datum, can be also the unsteady datum producing through internal calculation.Can carry out more neatly the comparison of signal like this.
As previously mentioned, alternatively, diode D can be also diode and the connecting of resistance.This resistance in series also plays the effect of current limliting, while preventing that DRAIN from being high level, excessive toward the forward current of vdd terminal from DRAIN end.
Alternatively, be to strengthen coupling, also can be in the drain electrode of JFET an external capacitive in parallel with source class.
Pressure drop unit 11a shown in Fig. 3 also can be applied in the demagnetization testing circuit scheme shown in Fig. 1.That is to say, the negative pole of diode D is connected to ground or low-voltage biasing, and is free of attachment to vdd terminal.
Fig. 4 shows another example of the demagnetization testing circuit principle based on shown in Fig. 2.With Fig. 2 contrast, the demagnetization testing circuit 10b shown in Fig. 4 has comprised that pressure drop unit 11b(is as shown in dashed rectangle).Compare in the example of Fig. 3 and use high voltage bearing technotron, the example of Fig. 4 has been used isolated gate FET MOS.As aforementioned principles, the resistance R of having connected between MOS and VDD.Wherein, the input end of MOS is connected with DRAIN, the Vx end of MOS is connected with one end of R, the input end of the other end of R and datum generating unit 12 is connected to VDD, the output terminal of datum generating unit 12 is connected to the normal phase input end of comparer 13, and the output terminal of MOS is connected to the inverting input of comparer 13.
Alternatively, also can adopt such connected mode, the output terminal of MOS is connected to the normal phase input end of comparer 13, and the output terminal of datum generating unit 12 is connected to the inverting input of comparer 13.
For the metal-oxide-semiconductor not being connected with source electrode for substrate, drain electrode, source electrode can exchange, if therefore using its source electrode as its input end, its drain electrode is output terminal, if drained as input end, its source electrode is output terminal.
In addition, as shown in Figure 4, the grid of MOS is connected to certain fixing bias voltage Vb.
When DRAIN is high level, the drain electrode of switching tube is powered to VDD by MOS and resistance R.Due to the hypotensive effect of MOS, at the output terminal (Vx end) of MOS, produce the low voltage signal of about tens volts.After inductive current is reduced to zero, there is ringdown in DRAIN, due to the coupling of the stray capacitance Cds between the source class of MOS and drain electrode, at Vx, holds and there will be an amplitude to reduce ringdown.When voltage Vx lower than by datum generating unit 12, generated threshold value Vref_DM time, represent that demagnetization end point detection has arrived, comparer 13 output signal Vout.Wherein, Vref_DM can be constant datum, can be also the unsteady datum producing through internal calculation.
As previously mentioned, the resistance R of series connection can play the effect of current limliting, while preventing that DRAIN from being high level on the one hand, excessive toward the forward current of vdd terminal from DRAIN end; When the drain terminal voltage Vd of tested switching tube is low level, reduce the power supply of VDD to DRAIN on the other hand, can keep better VDD constant like this.Alternatively, resistance R can be also diode or diode and the connecting of resistance.
In addition, as previously mentioned, the pressure drop unit 11b shown in Fig. 4 also can be applied in the demagnetization testing circuit scheme shown in Fig. 1.That is to say, one end of resistance R is connected to the output terminal of metal-oxide-semiconductor, the other end is connected to ground or low-voltage biasing, and is free of attachment to vdd terminal.
Alternatively, be to strengthen coupling, also can be in the drain electrode of MOS an external capacitive in parallel with source class.
Fig. 5 shows according to the basic circuit diagram of the non-isolation AC-DC LED driver of the embodiment of the present invention.As shown in Figure 5, driver 1A comprises: resistance R 1, capacitor C 1, sustained diode 1, inductance L 1, power MOS pipe M1 and sampling resistor Rs.Wherein, VM is the busbar voltage that civil power obtains after rectifier bridge rectification.Resistance R 1 and capacitor C 1 are connected on VM(bus) and ground between; The negative pole of sustained diode 1 is connected to positive pole and the VM of load LED; One end of inductance L 1 is connected to the positive pole of sustained diode 1, and the other end is connected to the negative pole of load LED; Power MOS pipe M1 is connected between inductance L 1 and sampling resistor Rs, and its drain electrode is connected to the positive pole of sustained diode 1, and source electrode is connected to sampling resistor Rs; One end of sampling resistor Rs is connected with the source electrode of power MOS pipe M1, other end ground connection.
In Fig. 5, VDD is chip internal power supply (pin), the driving signal pin that DRV is M1, and the drain terminal voltage pin that DRAIN is M1, and CS is reference voltage pin.Particularly, one end that resistance R 1 is connected with capacitor C 1 is connected with VDD, thereby is control circuit power supply, and capacitor C 1 is for chip power filtering; DRV is connected with the grid of M1, for driving M1; One end that sampling resistor Rs is connected with the source electrode of M1 (ungrounded end) is connected with CS, for control circuit provides current sampling signal.
After driver 1A starts working, power tube M1 conducting, electric current is from VM, through LED, L1, M1, Rs flows to ground, and electric current increases gradually, when the peak value of electric current reaches the threshold value (Vref) of setting, by peak current detection module, the control of the modules such as PWM controller, turn-off M1, now, inductance L 1 is passed through D1, LED carries out afterflow, when inductive current drops to zero, the demagnetization time of inductance L 1 by demagnetization testing circuit, detected, then via constant current algorithmic controller, the control of the modules such as PWM controller, in the specific time, make M1 conducting again, start the new cycle.So circulation, thus make the average current of exporting LED keep constant.In fact power MOS pipe M1 has played the effect of switching tube.
The sequential chart of Fig. 6 schematically shows the working condition under discontinous mode according to the AC-DC LED driver of the embodiment of the present invention.
As shown in Figure 6, when the control signal PWM of PWM controller 30 is while being high, driving stage 50 is by driving pin DRV driving power metal-oxide-semiconductor M1 conducting, and the drain electrode end DRAIN voltage Vd of M1 is low level, electric current from VM through LED, inductance L 1, power tube M1, resistance R s to ground.Inductive current IL increases gradually, and correspondingly the voltage CS of resistance R s also increases gradually.When CS pin voltage CS reaches predetermined threshold value Vref, peak current detector 40 is sent signal, and PWM is dragged down, final power tube M1 cut-off.At this, threshold value Vref can be constant datum, can be also the datum producing after constant current algorithmic controller 20 calculates.
After switching tube M1 cut-off, its drain electrode end DRAIN voltage Vd is elevated to the forward voltage of a high diode also than busbar voltage VM, and inductance L 1 forms a loop by sustained diode 1, LED series connection, and inductive current IL reduces gradually.
As previously mentioned, when inductive current IL is reduced to zero, resonance due to the stray capacitance of the demagnetization testing circuit (demagnetization detecting device) 10 in inductance L 1 and control circuit, can produce ringdown (being reflected in drain electrode end DRAIN voltage Vd) at the drain electrode end DRAIN of M1.Under the effect of pressure unit 11 of demagnetization detecting device 10, drain electrode end DRAIN voltage Vd is converted to output terminal (Vx end) the voltage Vx of pressure unit 11, thereby at the output terminal of pressure unit 11, produce the ringdown that voltage amplitude has reduced, as shown in Vx waveform in Fig. 5.Vx starts the time point of starting of oscillation, the end point of the time of demagnetizing exactly.
After demagnetization finishes, the output signal of comparer 13 of demagnetization detecting device 10 inputs to constant current algorithmic controller 20, through constant current algorithmic controller 20, controls, and inductive current remained after zero a period of time, then to make pwm signal be high, starts next cycle.
At PWM, be low moment, switching tube M1 cut-off, this time point is the starting point of demagnetization time, as demagnetized in Fig. 6 as shown in signal DM, the left rising edge of demagnetization time T DM is that corresponding PWM is low moment.
Meanwhile, due to the impact of some parasitic parameters of switching tube, may there is the burr that some are abnormal in Vd, and correspondingly Vx also may occur these burrs, sees the Vx waveform in Fig. 6, and this waveform exists burr phenomena in an initial part of demagnetization time T DM.Thus, alternatively, the false triggering for the detecting device 10 that prevents from demagnetizing, is set to demagnetization detecting device 10, after PWM is low, through one section of delay, starts to detect again.This delay is the lead-edge-blanking time, as shown in the LEB part in the STB waveform of Fig. 6.STB signal is window detection time of the comparer 13 of demagnetization detecting device 10.
The sequential chart of Fig. 7 schematically shows the working condition under critical current mode pattern according to the AC-DC LED driver of the embodiment of the present invention.
Compare with the discontinuous mode of Fig. 6, the difference of the working condition under critical current mode pattern of Fig. 7 is, the control circuit of LED driver 1A is set to, when inductive current being detected, be zero, the time of demagnetizing, PWM was set to height immediately during end point, started next cycle.Thereby inductive current do not remain for a period of time of zero, but after being reduced to zero, growth will begin in a minute.Under critical current mode pattern, the demagnetization testing circuit 10 of control circuit part is identical with the demagnetization testing circuit 10 under aforementioned discontinuous mode.
The control circuit that has comprised the demagnetization testing circuit of Fig. 1, Fig. 2, Fig. 3 or Fig. 4 can be applied to the non-isolation AC-DC LED circuit shown in Fig. 5 as previously mentioned, is equally also applicable to the isolation inverse-excitation type AC-DC LED circuit shown in Fig. 8.
The key distinction of the LED drive circuit 1A of LED drive circuit 1B shown in Fig. 8 and Fig. 5 is, has realized the isolation of drives side (former limit) and load-side (secondary) with transformer T.Particularly, as shown in Figure 8, LED drive circuit 1B comprises sustained diode 1 in the second coil side of transformer T, alternatively, also comprises filter capacitor C2; The demagnetization detecting device (circuit) of control circuit (chip) detects the inductance demagnetization time of transformer T.
Alternatively, different with the earth level of its second coil side at the earth level of primary side of transformer T, as shown in Figure 8.Because primary coil is connected on civil power high-pressure side, secondary coil is connected on output LED end, if adopt both not schemes on ground altogether, safer secondary (being generally low-voltage) like this.
Alternatively, power tube M1 can be high-voltage circuit breaker pipe, and its source-drain electrode is symmetrical, and one in source electrode or drain electrode is connected with the primary coil of transformer T, and another is connected with sampling resistor Rs.Power tube M1 can bear higher voltage like this.
Alternatively, transformer T is the isolating transformer of N:1, and wherein N is natural number.
LED drive circuit 1B can work in discontinous mode and continuous current mode pattern equally, and its principle of work sequential can be with similar shown in Fig. 6 and Fig. 7.
According to the demagnetization detection method of the embodiment of the present invention, demagnetization testing circuit and applied the constant-current drive circuit (comprising LED drive circuit) of this demagnetization testing circuit, can realize: due to the hypotensive effect of demagnetization testing circuit, by the high-voltage signal of power tube drain electrode, be reduced to low-voltage signal, for demagnetization time detecting realization condition is provided; With the circuit that low-voltage device forms, realized the detection of demagnetization end point.Alternatively, can also realize when the drain electrode of measured power pipe is high level, be control circuit (chip) power supply.
According to the demagnetization testing circuit of the embodiment of the present invention, by managing such as JFET or the device such as metal-oxide-semiconductor is realized, be easy to be integrated in integrated circuit (IC) chip, thereby as the part of the control chip of driving circuit, can simplify production technology, reduce production costs.
The above is only exemplary embodiment of the present invention, but not for limiting the scope of the invention, protection scope of the present invention is determined by appended claim.
Claims (14)
1. a demagnetization testing circuit (10), is characterized in that, comprising: pressure drop unit (11), and datum generating unit (12) and comparing unit (13), wherein,
Pressure drop unit (11) is connected with the drain electrode end (DRAIN) of measured power switching tube (M1), for reducing the voltage of the signal from this drain electrode end (DRAIN), and the drain signal after step-down (Vx) is sent to described comparing unit (13);
Datum generating unit (12) generating reference threshold value (Vref_DM), and this reference threshold (Vref_DM) is sent to described comparing unit (13);
The different input ends of described comparing unit (13) receive respectively drain signal (Vx) and the described reference threshold (Vref_DM) after described step-down, and described comparing unit (13) compares the drain signal after described step-down (Vx) and described reference threshold (Vref_DM), detect demagnetization end time point.
2. demagnetization testing circuit according to claim 1 (10), it is characterized in that, described pressure drop unit (11) is further connected between the drain electrode end (DRAIN) and internal electrical source (VDD) of measured power switching tube (M1), when the voltage of described drain electrode end (DRAIN) is high level, this drain electrode end (DRAIN) is described internal electrical source (VDD) power supply by described pressure drop unit (11).
3. demagnetization testing circuit according to claim 2 (10), it is characterized in that, described pressure drop unit (11) comprises voltage drop element (JFET, MOS), this voltage drop element (JFET, MOS) input end is connected with the described drain electrode end (DRAIN) of measured power switching tube (M1), its output terminal is connected to an input end of described comparing unit (13), and at described voltage drop element (JFET, MOS) between output terminal and described internal electrical source (VDD), be further in series with diode (D) and/or resistance (R), the positive pole of wherein said diode (D) is connected to described voltage drop element (JFET, MOS) side, its negative pole is connected to described internal electrical source (VDD) side.
4. demagnetization testing circuit according to claim 3 (10), is characterized in that, described voltage drop element (JFET, MOS) is technotron (JFET) or isolated gate FET (MOS).
5. demagnetization testing circuit according to claim 3 (10), is characterized in that, between the input end of described voltage drop element (JFET, MOS) and output terminal, is parallel with electric capacity.
6. demagnetization testing circuit according to claim 1 (10), is characterized in that, described reference threshold (Vref_DM) is constant datum or unsteady datum.
7. the control circuit driving for constant current, is characterized in that, comprising:
According to the demagnetization testing circuit (10) described in any one in claim 1-6, constant current algorithmic controller (20), PWM controller (30), peak detctor (40) and driving stage (50), wherein,
Described demagnetization testing circuit (10) is connected with the drain electrode (DRAIN) of the power switch pipe (M1) of described constant-flow driver, to receive the drain signal of described power switch pipe (M1), and this demagnetization testing circuit (10) sends a signal to described constant current algorithmic controller (20) after described demagnetization end time point being detected;
The demagnetization end time point that described constant current algorithmic controller (20) detects based on described demagnetization testing circuit (10) sends the first control signal to described PWM controller (30);
Described peak current detector (40) detects the source-drain electrode electric current of described power switch pipe (M1) by detecting the voltage of the sampling resistor (Rs) of described constant-flow driver, and to described PWM controller (30), sends the second control signal according to this current detecting result;
Described PWM controller (30) generates pwm signal based on described the first control signal and/or described the second control signal, and this pwm signal is sent to described driving stage (50);
The output terminal (DRV) of described driving stage (50) is connected with the grid of described power switch pipe (M1), with according to described pwm signal conducting or turn-off this power switch pipe (M1).
8. a constant-flow driver (1A), is characterized in that, comprising: resistance (R1), electric capacity (C1), fly-wheel diode (D1), inductance (L1), power switch pipe (M1) and sampling resistor (Rs), wherein, resistance (R1) and electric capacity (C1) are connected between bus and ground; The negative pole of fly-wheel diode (D1) is connected to positive pole and the bus of load light emitting diode (LED); One end of inductance (L1) is connected to the positive pole of fly-wheel diode (D1), and the other end is connected to the negative pole of load light emitting diode (LED); Power switch pipe (M1) is connected between inductance (L1) and sampling resistor (Rs), and its drain electrode is connected to the positive pole of fly-wheel diode (D1), and source electrode is connected to sampling resistor (Rs); One end of sampling resistor (Rs) is connected with the source electrode of power switch pipe (M1), other end ground connection, and described driver (1A) also comprises control circuit according to claim 7.
9. constant-flow driver according to claim 8 (1A), it is characterized in that, if this constant-flow driver (1A) works in discontinous mode, when the pwm signal of described PWM controller (30) is while being high, described driving stage (50) drives described power switch pipe (M1) conducting, the drain voltage of described power switch pipe (Vd) is low level, electric current from bus through light emitting diode (LED), inductance (L1), power switch pipe (M1), sampling resistor (Rs) is to ground, the electric current (IL) of inductance (L1) increases gradually, correspondingly the voltage (CS) of sampling resistor (Rs) also increases gradually, when sampling resistor voltage (CS) reaches predetermined threshold (Vref), described peak current detector (40) is sent described the second control signal to described PWM controller (30), described PWM controller (30) drags down pwm signal, make described power switch pipe (M1) cut-off, described pwm signal is that low time point is the starting point of demagnetization time, after described power switch pipe (M1) cut-off, its drain voltage (Vd) raises, and described inductance (L1) is connected with described fly-wheel diode (D1) and described light emitting diode (LED) and formed a loop, and inductive current (IL) reduces gradually, when inductive current (IL) is reduced to zero, at the drain electrode generation ringdown of power switch pipe (M1), described demagnetization testing circuit (10) detects this ringdown, thereby the end point of demagnetization time detected, detect demagnetization finish after, described demagnetization testing circuit (10) outputs signal to described constant current algorithmic controller (20), at inductive current (IL), remain after zero a period of time, described constant current algorithmic controller (20) sends described the first control signal to described PWM controller (30), makes described pwm signal for high, starts next cycle.
10. constant-flow driver according to claim 9 (1A), is characterized in that, described demagnetization testing circuit (10) is set to, and after described pwm signal is low, through one section of delay, starts to detect again.
11. constant-flow drivers according to claim 8 (1A), it is characterized in that, if this constant-flow driver (1A) is in critical current mode pattern, described control circuit is set to, when the electric current (IL) of described inductance (L1) being detected, be zero, described pwm signal is set to height immediately, starts next cycle.
12. 1 kinds of constant-flow drivers (1B), is characterized in that, comprising: resistance (R1), electric capacity (C1), fly-wheel diode (D1), power switch pipe (M1), sampling resistor (Rs) and isolating transformer (T), wherein, resistance (R1) and electric capacity (C1) are connected between bus and ground; The armature winding of isolating transformer (T) is connected between described bus and described power switch pipe (M1), and its secondary winding is connected with the positive pole of fly-wheel diode (D1); The negative pole of fly-wheel diode (D1) is connected to the positive pole of load light emitting diode (LED); Power switch pipe (M1) is connected between the armature winding and sampling resistor (Rs) of isolating transformer (T), and its drain electrode is connected to the armature winding of isolating transformer (T), and source electrode is connected to sampling resistor (Rs); One end of sampling resistor (Rs) is connected with the source electrode of power switch pipe (M1), other end ground connection, and described driver (1B) also comprises control circuit according to claim 7.
The detection method of 13. 1 kinds of inductance demagnetization times, is characterized in that, comprising:
Reduction is from the voltage of the signal of measured power switching tube drain electrode;
Generating reference threshold value; And
By the drain signal of described lower voltage and described reference threshold comparison, detect demagnetization end time point.
14. inductance according to claim 13 demagnetization time detecting methods, is characterized in that, the amplitude of the drain signal of described lower voltage during lower than the amplitude of described reference threshold, detects described demagnetization end time point.
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